The human eye has three concentric layers of tissue enclosing the lens and the inner media. The eyes outermost covering is the tough, fibrous sclera and its anterior transparent modification, the cornea. The cornea is the major light refractor of the eye. Below the sclera is the pigmented vascular layer of the eye, which includes the choroid, ciliary body and the iris.
The vitreous cavity constitute two-thirds (⅔) of the volume of the eye. It is filled with transparent jell, the vitreous humor. The portion of the eye in front of the vitreous is divided into two compartments, the anterior chamber (between the cornea and iris) and the posterior chamber (between the iris and vitreous). The chambers are filled with aqueous humor. The innermost layer of the eye, or sensory retina, lines the posterior two-thirds (⅔) of the globe and has several distinct histologic layers.
The natural lens of the eye comprises a transparent envelope, called the capsular bag, which contains the crystalline structure and is suspended by the zonules from the surrounding ciliary body. The front and rear walls of the capsular bag are known as interior and posterior capsules, respectively.
The ability of ciliary muscle to contract and the lens to become more convex is called accommodation which increases the ability to see near objects. With increasing age, the lens of every eye undergoes a progressive hardening, with loss of ability to change its shape. Loss of accommodation is manifested by a decreased ability to focus on near objects (commonly referred to as presbyopia), while corrected distance visual acuity remains normal.
Accommodation is thus the natural process by which the lens of the eye can increase the curvature of its front and back surfaces and thereby change its refractive power in order to adjust from distance vision to near vision. This typically occurs in response to contractions of the ciliary muscle.
A cataract is any opacity or discoloration of the lens whether a small, local opacity or the complete loss of transparency.
Clinically, the term cataract is usually reserved for opacities that effect visual acuity. The most common cause of cataract is age related change.
Other causative factors include inflammation, trauma, metabolic and nutritional defects, and radiation damage. Cataracts may develop very slowly over the years or may progress rapidly depending on the cause and the type of cataract.
The cataracts may be in both eyes and, being a progressive condition may cause fading vision and eventual blindness. If a cataract interferes with patient's daily pattern of living, the patient may benefit from cataract extraction, which can be performed using many different surgical techniques.
Cataracts were once surgically removed along with the interior wall of the capsule of the eye. The patient then wore eye glasses or contact lenses which restored vision but did not permit focusing and gave only limited depth perception.
The first implant of a replacement lens within the eye occurred around 1949 and attempted to locate the replacement lens in the posterior chamber of the eye behind the iris. Problems such as dislocation after implantation forced abandonment of this approach, and for some period thereafter intraocular lenses were implanted in the anterior chamber of the eye. Lenses implanted in the anterior chamber of the eye were of various designs.
Others returned to the practice of inserting the lens in the area of the eye posterior to the iris, known as the posterior chamber. This is the area where the patient's natural crystalline lens is located. When the intraocular lens is located in this natural location, substantially normal vision may be restored to the patient and the problem of forward displacement of the vitreous humor and retinal detachment encountered in anterior chamber intraocular lenses are less likely to occur. Many designs of lenses for implantation in the posterior chamber have been proposed. However, most of these designs suffer from lack of sharp variable focusing capability.
The prior art has proposed some examples of lenses of capable of focusing thus offering the wearer the closest possible substitute to the crystalline lens. However, the prior art accommodative lenses suffer from numerous drawbacks including overall complexity leading to increased costs and decreased overall reliability. Accordingly, there exists a need for an improved intraocular lens implant having accommodative capabilities.